Experimental and theoretical electron energy spectra due to ionizing collisions of metastable Ar*(³P₂), Ar*(³P₀) and Kr*(³P₀) atoms with ground-state Hg atoms

Abstract

Using a crossed-beams set-up, we have studied the electron energy spectra due to Penning and associative ionization in thermal energy collisions of stateselected metastable Ar * 4s 3 P 2 , 3 P 0 and Kr * 5s 3 P 0 atoms with ground-state Hg atoms at an electron energy resolution of 30 meV. In all three cases the energy spectra exhibit a prominent peak located close to the energy difference between the metastable excitation energies and the Hg ionization energy; they show a sharp drop to lower and an extended tail towards higher electron energy with shapes which differ for the three systems. The energy-integrated ionization cross section for Ar * 3 P 0 exceeds that for Ar * 3 P 2 by about 30%. Excitation transfer to autoionizing Hg * * states, resulting in a sharp additional structure, is only observed-as a weak channel-in Ar * 3 P 0 + Hg collisions. For the three investigated systems calculations of the electron energy spectra have been carried out within the local optical potential approximation. As input we use ab initio potential curves for the ionic exit channels as well as for the complex entrance channel potentials. Using these potentials (involving a scaled width for Kr * + Hg), impressive agreement with the experimental electron spectra is observed. In contrast, earlier empirical model potentials for the entrance channel are found to be inadequate. The calculated ionization rate coefficients at T = 300 K amount to (3.72, 5.26) × 10 −10 cm 3 s −1 for Ar * 3 P 2 , 3 P 0 + Hg, respectively.

Optical Quenching of Metastable Helium Atoms using Excitation to the 4P State

“…In this scheme, the population of one metastable state is transferred to the electronic ground state via optical excitation to a higher-lying electronic state, whose decay to the electronic ground state is strongly allowed for electric-dipole radiation. There exist efficient optical pumping schemes for atomic beams of metastable helium, neon, argon and krypton [21,[25][26][27][28][29][30][31][32][33]. The de-excitation of metastable helium atoms in the 2 1 S 0 state has thus far only been attained in a supersonic beam by illuminating the atomic beam with 2058 nm light from a helium discharge lamp, which is resonant with the 2 1 P 1 ← 2 1 S 0 transition [25][26][27][28]34].…”

Metastables as a probe for low-temperature plasma characteristics in argon

“…Here, m (Ar) is the excitation energy to Ar(1s 5,3 ), and i (X) is the ionization energy of a molecule X. kin is the kinetic energy of the ejected electron. Table 3 includes the Penning ionization rate coefficients between Ar(1s 5,3 ) and ground-state Hg; the total de-excitation rates are added for comparison [35]. The lowest ionization energy of C 2 H 2 ( 1 Σ + g ) is estimated at 11.4 eV [36], and the system between Ar(1s 5 ) and C 2 H 2 ( 1 Σ + g ) may set up the Penning ionization (8).…”

“…Penning ionization and total quenching rate coefficients, k PI and k Tq , of Ar(1s 5 ) and Ar(1s 3 ) with Hg atom at 300 K[35].k PI (cm 3 s −1 )k Tq (cm 3 s −1 )Ar(1s 5 )3.72 × 10 −10 8.49(±20%)×10 −10 , 4.3(±35%)×10 −10 Ar(1s 3 ) 5.26 × 10 −10 9.56(±20%)×10 −10 , 8.4(±35%)×10 −10…”